RP-23 experts needed - again

LV can and service kit came today. Easy enough to change the cans - just as you all said it would be.

Since I had 700+ miles on the shock, I got the service kit too. I replaced the upper body seal and backup rings, the new LV can came with wiper and seals already installed. Screwed everything together with the healthy dose of Float fluid, pumper her up to 200 psi and now I swear I have a slight scraping sound on the inside. The noise is on initial stroke only, if I'm on the bike and load the suspenion past the sag point, no scraping noise.

My gut said a backup ring was lightly scraping the inside of the LV can on initial stroke. Unscrewed everything, couldn't find anything amiss, no markings on the inside of the can, nothing on the exposed shock piston - some bubbly float fluid (is it supposed to bubble - I would think it would resist bubbling to provide consistency like automatic tranny fluid) but nothing out of the ordinary. When I installed the new backup rings and upper body (quadrangle?) seal, the upper ring was gapped a bit more than the lower one, though, in my opinion, it didn't stick out there far enough to prevent the seal from working. Every new seal was lubed really well so it's not stiction.

My only other theories are cavitation noise or a cable stop somewhere between the top tube and seatstay. I'm pretty positive it's neither, the cable stop sounds a bit different and cavitation of the fluid, in my uneducated guess, be present throughout more of the stroke.

I suspect this backup ring will eventually seat itself or the edge that slightly rubs will wear in - it's holding air, working fine, just the type-A homer in me can't stop obsessing over this minor noise (which I can't hear over the noise of my Hope hub

Any wisdom from the shock gurus?

Happiness depends more on the inward disposition of mind than on outward circumstances. Benjamin Franklin

There is a small dimple pressed into the air sleeve near the lower wiper lip that allows air to escape past the air piston head when the shock extends to equalize the pressure between the positive and negative air chambers. Float fluid will get sucked along with the moving air and create a short, sharp wheezing noise as the chambers equalize. That may be what you are hearing. That is what causes the lube fluid to foam too. Shocks do this less over time because the lube fluid migrates out of the shock past the wiper.

Out of curiosity, I replaced the upper backup ring with the old one, noise is reduced a little. My new theory is the canister itself is just a bit narrow at top, and with some extended use, the rings will bed in and the noise will stop.

I was able to isolate the cable stops and eliminate that as a source.

Happiness depends more on the inward disposition of mind than on outward circumstances. Benjamin Franklin

There is a small dimple pressed into the air sleeve near the lower wiper lip that allows air to escape past the air piston head when the shock extends to equalize the pressure between the positive and negative air chambers. Float fluid will get sucked along with the moving air and create a short, sharp wheezing noise as the chambers equalize. That may be what you are hearing. That is what causes the lube fluid to foam too. Shocks do this less over time because the lube fluid migrates out of the shock past the wiper.

I wondered what that dimple was for. While I had it off last - I removed a little float fluid (used more than the 2cc the Fox video said w/ an overzealous squeeze on the pillow pack) so that may be what helped the noise a bit.

Thanks for the feedback.

Happiness depends more on the inward disposition of mind than on outward circumstances. Benjamin Franklin